Miniature-3 (mn3): a viable miniature kernel mutant on chromosome 6

Philip S. Stinard

A small kernel mutant tightly linked to y1 was found segregating on the selfed ear of a plant (86-1184-8) grown from the cross Y1 Y1 X y1 y1-pastel(Mu). Seedling tests of white kernels from the segregating ear indicated that the mutant, originally designated de*-1184, was in coupling with the standard y1 allele, and not the putative Mu-induced y1 pastel allele. Mutant kernels of de*-1184 are smaller than wildtype, ranging in size from near normal to nearly empty pericarp, and have etched/pitted endosperm. There is a tendency for mutant kernels to lack germs, but many mutant kernels have healthy germs, and give rise to green, normal-appearing plants. Upon self-pollination, these plants produce all mutant kernels. Because there are no mutants with similar phenotype on chromosome 6, we have given de*-1184 the name miniature-3 (mn3).

Crosses of known heterozygotes of mn3 by TB-6Lc and TB-6Sa produce only normal sized kernels, indicating that mn3 is proximal to the TB breakpoints on chromosome 6. Three-point linkage tests of mn3 with the chromosome 6 linkage stocks w15 y1 and y1 l15 were made as indicated in Tables 1 and 2. Plants grown from the testcrosses were self-pollinated, and the resultant ears scored for y1 and mn3. Kernel samples from the selfed ears were planted in the sandbench, and the resultant seedlings scored for w15 or l15. These tests give the following linkage relationships: mn3-4.4-w15-2.5-y1 and mn3-2.1-y1-7.7-l15. The mn3-y1 distance is greater in the mn3 w15 y1 cross (6.9cM) than in the mn3 y1 l15 cross (2.1cM). The y1-l15 distance (7.7cM) does not agree with distance for the same interval on the 1990 linkage map (13cM), but the w15-y1 distance (2.5cM) does. The linkage distances in the mn3 y1 l15 cross seem to be smaller than they should be. The reason for this is not known, but could be due to the different genetic backgrounds of the two linkage stocks. It is likely, therefore, that the mn3 w15 y1 data better reflect the true linkage relationships, at least with respect to the established linkage map of chromosome 6. If this is the case, then mn3 is located at map position 10, in the vicinity of Mdm1. Until additional linkage studies are conducted to verify the order of mn3 and Mdm1 on the chromosome 6 map, the suggested map revision is:

                 mn3
rgd1----Mdm1---w15-------y1------------l15
   8             11           13            17                  30


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